Water soluble dyes are generally liquids, or soluble solids which are used in solution. Pigments, are generally solids and are usually insoluble in the medium in which the pigment is being used. Water soluble dyes have significant disadvantages when used in soaps and toothpastes, for instance as these dyes can stain skin, and clothing and often complex with proteinaous materials. Further, as the soap bars and toothpaste contact water repetitively, the water-soluble dyes tend to run and stain sinks, bathtubs, etc. Pigments, are therefore, typically used instead of dyes in applications where color migration or bleeding is undesirable.
Various approaches have been proposed to reduce the bleeding or staining of lakes and dyes to prevent migration of the color into the surrounding phases. These resultant products are used in household and toiletries products such as soap, toothpaste, and other cosmetics.
Absorption of the lake onto a medium, a colorless substrate of alumina, zirconia, or titania in this instance, is taught in U.S. Pat. No. 4,444,746. The alumina, zirconia, or titania is used to absorb the pigment onto their surfaces, which provides a means for dispersion of the color throughout the dentifrice medium, without dissolution of the water-soluble dye.
Water insoluble pigments and production thereof is disclosed in U.S. Pat. No. 4,769,080 in which a layered anion exchange material is contacted with the dye under conditions in which a water-insoluble pigment is obtained. The water soluble dye and the layered anion exchange material are contacted together in a liquid medium in which the dye has been dissolved. The layered anion exchange material is preferably a layered aluminate.
GB Patent 1,319,991 discloses preparation of colored resins with non-toxic water soluble dyes as a water impervious cross-linked synthetic resin for use in toothpastes. The polymerized resins which are used in this process have monomers which are soluble in water and can be polymerized to insoluble resins in an aqueous solution. The resins employed in this disclosure do not take up appreciable water on prolonged contact. Specifically, low molecular weight water soluble resins such as urea formaldehyde, melamine formaldehyde, melamine-urea formaldehyde and phenol formaldehyde resins are described.
U.S. Pat. No. 4,129,638, U.S. Pat. No. 4,202,878, and GB 1,319,992 all disclose preparation of a pigment in an agglomerate form whereby the pigments are dispersed in molten wax, or a gelling agent which is then reduced in particle size to 200 to 500 microns. The pigment particles must be color-fast and water-soluble dyes per se, and can not be used in this invention. However, the disclosure teaches use of color fast dyed thermo-setting resin particles, as described in GB 1,319,991 above.
U.S. Pat. No. 4,069,311 discloses prior art procedures by which speckles have been prepared by melting a physiologically acceptable organic binder, such as a thermoplastic resin, wax or high molecular weight ester, e.g., glyceral tristearte. This prior art method of converting the resultant particles, which are somewhat irregular in appearance and size, to particles in the range of 0.05 to 1 mm can be obtained through tedious and costly screening or sieving. To avoid the irregular shape and screening the patent teaches use of high shear agitation of the speckling material, and a binder, such as thermoplastic resins, gums, gels, paraffin's, waxes, polymers, and higher fatty acids and salts thereof, with dispersion of the molten mixture of binder and dye into a dispersing medium, such as water, thereby forming small globules or particles upon cooling.
Another approach for using non-toxic water soluble dyes is taught in U.S. Pat. No. 4,533,484 in which water-insoluble pigments were produced by contacting the water soluble dye with a polymer comprising an alkyl-2-oxazolidinone moiety. This resulted in a pigment particle have insolubility characteristics of the polymer and color characteristics of the dye. The pigmented polymer is prepared by contacting the polymer with an aqueous medium in which the polymer is at least partially soluble. To this solution, the dyes are added in excess. The temperature is raised and a highly colored precipitate results which may be filtered or dried. The polymer-dye yields a pigment which is insoluble in an aqueous liquid, at temperatures above 3.degree. C. A pigment is generally insoluble in an aqueous medium under normal conditions of use.
The prior art methods have failed to produce a product, particularly a product which has small particle size, which effectively prevents the migration of the color into the surrounding medium. The present invention provides such a method in a commercially practicable, and useful method whereby the prepared matrix particle is useful for any lake of a soluble dye that left untreated would tend to leach in water or other solvent.